1. Field of Invention
This invention relates to electrical interconnection circuitry, and more particularly to circuitry providing electrical interconnection from a rotating body to a relatively stationary body.
2. Description of the Prior Art
In an electrical system requiring the electrical interconnection of a rotating body to a relatively stationary body, the reliability of such an interconnection is determined by its weakest element, namely the mechanical component providing the electrical interconnection between the rotating member and the stationary member. The degree of importance placed upon the reliability of the interconnection is directly related to the ultimate system function, and such systems as those performing safety functions whose ultimate objective is the prevention of human injury or loss of life must necessarily have the highest degree of reliability. One example of such a system is that used in helicopter aircraft for monitoring the structural integrity of the helicopter rotor blades. This parameter, which is so essential to the airworthiness of the aircraft, requires a monitoring system with a high degree of reliability to assure the detection of a structural failure when it occurs. Also, due to the low frequency of occurrence of such a structural failure, the system must minimize the occurrence of erroneous failure indications which destroy system credibility (causing valid failures to be ignored) or which may initiate unnecessary emergency procedures. Due to the difficulty of providing a reliable rotating interconnection, some prior art methods of checking the structural integrity of the helicopter rotor blades have been limited to visual inspection of the individual blades while the aircraft is on the ground, and the rotor is in a static condition. A more detailed method of blade inspection is disclosed in a patent to R. A. Parr, U.S. Pat. No. 3,667,862 wherein the spar assemblies which mount the airfoils to the rotor head are hermetically sealed and evacuated. Pressure transducers are used to sense the vacuum; however, the transducer is only used to provide an indication during ground testing of the aircraft with the rotor again in the static condition. Under both of these methods potential failures resulting from dynamic operation of the rotor blade assemblies cannot be detected during flight.
A system for monitoring the structural integrity of individual rotor blades while the aircraft is in flight is disclosed in a patent to Jensen, U.S. Pat. No. 3,547,555. In this system, the individual spar assemblies connecting each blade to the rotor assembly are hermetically sealed and pressurized to an internal ambient pressure above atmosphere. Pressure transducers mounted on the individual spar assemblies monitor the internal ambient pressure and provide a discrete signal to a monitoring system within the aircraft cockpit for a reduction of the ambient pressure within the spar due to a loss of the spars structural integrity, thereby providing an indication of the detected failure to the pilot. That system uses a rotary transformer to conduct the discrete signal, provided by the pressure transducers, from the rotating blade assembly to the aircraft structure. The closing of a contact in the pressure transducer causes a change in the reflected impedance of the transformer primary winding, which causes an indicator to warn the pilot of potential failure. This system suffers from the disadvantage of using a single rotary transformer which is mechanically unreliable under constant rotational use, with the further disadvantage of requiring a relatively complex electrical circuit for detecting the transformer impedance change, which causes a reduction in the electrical reliability of the system due to the number of electrical components required. In summary, the prior art has failed to provide high reliability monitoring of the structural integrity of helicopter rotor blades, due to the lack of a highly reliable electrical interconnection between the rotor assembly and the aircraft structure.